Craniosynostosis, the premature fusion of calvarial sutures, is a common developmental anomaly that causes abnormal head shape. In moderate to severe cases, there is increase intracranial pressure and neurological sequelae, if not surgically treated. Craniosynostosis is a feature of as many as 50 genetic syndromes. Limb abnormalities, such as syndactyly and brachydactyly, are common associated features of these conditions. Crouzon, Jackson-Weiss, and Pfeiffer syndromes are autosomal dominant, craniosynostotic conditions with a wide variability of expression. We ascertained families with these conditions to study their chromosomes and/or DNA from established lymphoblastoid or fibroblast cell cultures. Fibroblast growth factor receptor 2 (FGFR2) mutations have been found in these conditions. We studied 39 cases with one of these three conditions for FGFR2 exon llla or exon lllc previously reported only in Crouzon syndrome are present also in one of the other two syndromes. Two insertions, one in exon llla in a Crouzon syndrome patient and the other in exon lllc in a Pfeiffer syndrome patient, were observed. The latter mutation has the same alternative RNA splicing effect as a reported synonymous mutation for Crouzon syndrome. A missense mutation, V359F, was detected in a family with one member with craniosynostosis and broad digits, diagnostic of Pfeiffer syndrome, and with two member with features consistent with Crouzon syndrome, craniosynostosis without limb anomalies. The inter-and intrafamilial variability in expression of FGFR2 mutations suggests that these three syndromes, presumed to be clinically distinct, are instead representative of a spectrum of related craniosynostotic and digital disorders.